Method of producing a nonagglomerating char from a strongly caking coal



United States Patent 3,355,363 METHOD OF PRODUCING A NONAGGLOM- ERATING CHAR FROM A STRONGLY CAK- ING COAL Stanley J. Gasior, Pittsburgh, and Albert J. Forney, Coraopolis, Pa., assignors to the United States of America as represented by the Secretary of the Interior No Drawing. Filed Feb. 14, 1964, Ser. No. 345,053 9 Claims. (Cl. 201-9) ABSTRACT OF THE DISCLOSURE A nonagglomerating char is produced from a particulate caking coal by contacting the coal in a fixed bed at its initial softening temperature with a gas containing small quantities of oxygen for a period of one to three hours.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention relates to treatment of caking coals to form a nonagglomerating char.

As natural gas reserves in the United States continue to dwindle, the most likely substitute is a synthetic high- B.t.u. gas produced from coal. Presently, fixed-bed pressure gasification appears to be most attractive for producing a high-Btu. gas. A gas with high methane content may thus be made with low oxygen requirements. Previously, however, strongly caking coals could not be gasified in this manner since they agglomerate when heated through a temperature range at which they become plastic, rendering the gasifier inoperable. Coals from the vast deposits in the East and Midwest, where the largest markets for a high-Btu. gas exist, are highly caking.

Existing commercial producers of noncaking coal-chars require mechanical devices such as a rotating kiln, chain grates, jiggling grates, rotating screws, etc., to prevent the strongly caking coals fiom fusing into one solid mass while being taken through the plastic temperature range. These devices necessitate ldgh capital investment.

Fluidized bed processes, such as that disclosed in US. Patent No. 2,805,189, in which the fluidized bed is treated with an oxygen-containin g gas have also been employed to prevent agglomeration of coal in processes such as carbonization, gasification, hydrogenation, etc. These fluidized bed processes have the disadvantage that the coal size is critical, and in addition require a costly briquetting step to increase the size of the small particles of char produced in the fluidized treatment. Another disadvantage of the fluidized bed process is that the treating gas velocity is critical, thus placing a strict operational limitation on fluidized treatment.

Previous attempts to produce a noncaking char in a fixed bed, Without the use of mechanical devices as described above, have met with little success.

It is therefore an object of the present invention to provide a fixed bed process for producing nonagglornerating char from a strongly caking coal that is simple, noncritical and inexpensive.

Patented Nov. 28, 1967 It has now been found that this object may be accomplished by means of a controlled heating of the caking coal in an atmosphere of an inert gas that contains a small amount of oxygen. It has been found that the coal must be treated with the oxygen-containing gas for a period of time at its initial softening and swelling temperature prior to being heated through its plastic temperature.

As indicated by the terms, the initial softening and swelling temperature is that temperature (or range of temperatures) at which the particles of coal begin to soften, swell and thereby fill the voids between the particles of coal. Conventional tests for determining this temperature utilize a flow of gas through the coal, the softening and swelling temperature being indicated by an increase in the differential pressure across the fixed-bed of coals due to filling of the aforementioned voids between the coal particles.

Following this treatment at the softening and swelling temperature, the coal particles may be taken through their plastic temperature range, i.e., the temperature at which the coal becomes plastic and resembles a paste or dough in which the particles flow within each other, in a fixed bed without caking, fusing or agglomerating. The coal particles may then also be exposed to a hydrogen-rich atmosphere at elevated temperatures and pressures in a fixed bed to produce a high-Btu. gas without agglomeratmg.

It has been found that a process in which the coal is rapidly heated to its initial softening and swelling temperature and then held at this temperature for a period of time in an atmosphere of inert gas containing a small amount of oxygen generally gives very satisfactory results. The period of time will depend on the type of coal treated as well as the amount of coal, particle size, treatment gas, etc., and is best determined empirically. It has been found that a period of treatment of about 3 hours is sufficient to prevent agglomeration in the case of the Pittsburgh seam coal employed in the examples below. Different time periods may be optimum for other types of coal, e.g., high volatile B bituminous Illinois No. 6 requires only about minutes while for Pocahontas No. 4, a low volatile bituminous coal, a period of about minutes is optimum, as compared to 180, and 200 minutes, respectively, for the high volatile A bituminous coals from the Upper Freeport, Taggart and Sewickley seams. Treatment times in the range of l to 3 hours have given satisfactory results for the coals tested. The coal may then be rapidly heated through its plastic temperature in the same atmosphere. The softening temperature and plastic temperature will usually encompass a range of temperatures and will vary considerably with the type of coal treated but may be readily determined by those skilled in the art if not previously known. The source, analysis, free swelling index, initial softening and maximum pretreatment temperatures are shown in Table 1.

Alternatively, coal may be effectively pretreated by rapid heating to its softening temperature in the oxygencontaining inert atmosphere followed by prolonged heating, as for example about 3 hours, through its plastic range in the same atmosphere.

TABLE 1.-SOURCE, ANALYSIS, FREE SWELLING INDEX, INITIAL SOFTENING AND MAXIMUM PRETREATIAENT TEM- PERATURES OF GOALS TESTED Proximate, percent Ultimate, percent Initial Free Maximum County, bed, mine softening swelling pretreatment Moisture Volatile Fixed Ash H C N O S temp, C. index temp., C

matter carbon Illinois Franklin, Illinois No. 6, Ben

Pennsylvania Allegheny, Pittsburgh, U.S.

BuMines Experimental 2. 5 35. 6 54.3 7. 6 5. 3 75. 8 1. 5 8. 2 1. 6' 360 8. 5 430 Butler, Upper Freeport, Coal Hollow No. 2 1. 7 35. 3 55. 9 7. 1 5. 3 76. 9 1 5 7. 9 1. 3 350 8. 0 430 Virginia Wise, Taggart, Dixiana 1. 4 33. 8 62. 3 2. 5 5. 3 82. 8 1. 5 7. 2 0.7 360 8.5 430 West Virginia McDowell, Pocahontas No. 4,

Bartley No. 1 u 2. 7 14. 8 76. 5 6. 0 4. 4 83.3 1. 3 4. 5 0. 5 470 6.5 .510 Monongalia, Sewickley, Christopher N0. 5 1.1 36.7 50.9 11.3 5.1 73.3 1. 5 6.2 2. 6 360 8.0 430 It has additionally been found that the pretreatment techniques as developed at atmospheric pressure works equally well at pressures up to 300 p.s.i.g. Optimum prescaking coal from a Bruceton, Pennsylvania mine having the analysis given in Table 3, below, and a particle size of about A. x /2 inch was used in Tests Nos. 1, 2, 3, 5,

sure will also vary with the type of coal, amount, particle 7, 9 and 11. Coal having a particle size range of about size, treatment gas, etc. /a to about 1 /2 inches is satisfactory for use in the proc- The specific composition of the gas used in the preess. The coal used in the other examples is shown in Table treatment is not critical except that it must contain the 2. The coal was treated in a fixed bed in a 3 /2 diameter required small amount of oxygen. The optimum amount vessel with a bed height as shown in Table 2. In the of oxygen will also depend on the type of coal, as Well 39 examples the treatment gas entered the bottom of the as other variables discussed above, and is best determined reaction vessel and passed upwardly through the bed empirically. Generally, the oxygen content will be in the of coal at atmospheric pressure. Gas velocity .through range of about 0.5 to about 3.0%. For economic purposes the coal bed may range from about 0.6 to about 12 feet a source of cheap inert gas such as flue gas, steam, carbon per second. However, treatment of the coal with .gas passdioxide, or nitrogen, containing some air or oxygen is ing downwardly through the bed has been found to be preferred. equally successful.

The invention is more specifically described but is not Analyses of the 30311 used in tests and the coal or intended to be limited by the following examples. ChaTPmdl-wed In the Prliltmatmem are given in Table The inert gas used to quench the coals in Examples 2, 4, Examples 1-11 6, 8, 10 and 11 was a mixture of 88 percent nitrogen and l I 12 percent carbon dioxide with a trace of'oxygen. Other Reactants, reaction conditions and results of these exinert gases such as nitrogenalone could be used for this amples are given .in Table 2. A Pittsburgh seam strongly purpose.

TABLE 2 Test Coal charge, Bed Type of treat. No. grains height, gas and a1nt., Treatment Conditions Results inches s.c;f.h.

1 600 6 Steam-+0 Coal heated from 30to 360 C. in%hr.with steam plus oxygen No iusion. No an arent we ht 300+3. then cooled to 100 C with N2 in hr. loss. Coel'appeziied same Es V p char ed.

2 60o 6 Steam+0z, Coal heated irom 30 to 360 C. in hr., then to 430 C. in 3 hr. No tus ion. 18.5% weight loss. B d

800+3. with steam plus oxygen; cooled to 100 C. in y, hr. with inert expanded Char flowered as gas. a freely as raw coal. 3 6 Air, 300 Coal heated to 200 C. 1n hr., held at 200 C. for 16 hr., then N 0 iusion;no apparent wei ht loss.

cooled to 100 C. in A hr., with air. Coal appeared same as charged. 4 Coal from 4 Steam, 300.- Coal heated from 30 to 430 C. in min. with steam; cooled to Char fused into one solid mass of '22s; No. 3, 100 C. in hr. with inert gas. highly porous char. 5 2 000: 20 Air 400 Coal heated from 30 to 300 C. in 3 hr. and held at 300 C. for No usion. 3.5 wei ht 10 s. C l

8 hr; then cooled to 100 C. in hr. with air. appeared site as charg ed. on 6 Coal from 6 Steam+0z, Coal heated from 30 to 430 C. in 75 min. with steam and Oz, Char fused into one solid mass No. 5, 400+5. then cooled to 100 C. in hr. with inert gas. with some discernible particles.

7 600 6 Air 500 002.1 heated from 30 to 340-350 C. in 2 hr. and held at 340 No fusion. 4.5 We htl ss. 0 l

I 350 C. for 8 hr., then cooled to 100 C. in hr. with air. appeared sazie as gzharged. 0a 8 Coal from 5 Steam-l-O Coalheated from 30 to 430 C. in min. with steam plus 02, Char fused into one solid mass test No. 7 +5. then cooled to 100 C. in hr. with inert gas. with some discernible particles. 9 60o 6 Air, 300--." Coal heated to 200 C. in hr.; held at 200 C. r 16 hr., then N0 fusion: no apparent Weight cooled to 100 C. in hr. with air. loss. Coal appeared srnae as char ed. 10 Coal from 4 Steam+0;, Coal heated from 30 to 430 C. in 75 min. with steam plus 1% Coal f sed into one solid mass of iesot No. 9, 300+3. oxygen; then cooled to 100 C. in hr. with inert gas. highly porous char. 11 600" 6 Steam+0z Coal heated from 30 to 360 C. in 15 n'iin.; held at 360370 C. No fusion; 18.4 weight loss. Cl 300+3. for 180 min. then heated to 430 in 30min. with steam plus 1% flowed as freely as coul. ml

oxygen. Char cooled to 100 C. in hr. with inert gas.

TABLE 3 Components Pittsburgh 1 2 3 5 7 8 9 10 11 seam PGH Moisture 1. 4 0. 5 0. 6 0. 3 0. 4 0. 5 0. 3 0. 5 0. 7 0. 7 Volatile matter-.. 37. 35. 7 20. 1 37. 36. 9 35. 1 36. 1 37. 5 25. 4 20. 2 Fixed carbon 57. 0 57. 0 70. 9 57. 0 56. 7 58. 7 56. 3 57. 0 66. 3 73. 2 Ash 4. 6 6. 8 8. 4 5. 2 6. 0 5. 7 7. 3 5. 0 7. 6 5. 9 H 5.4 5.1 4.1 5.1 4.8 4.6 5.0 5.1 4.6 4.1 C 79. 6 78. 7 77. 9 77. 8 77. 0 76. 8 77. 7 77. 8 77. 8 79. 7 N 1.6 1.6 1.8 1.6 1.6 1.7 1.6 1.6 1.8 1.8 O 7.8 6.2 6.4 9.3 9.4 10.1 7.2 9.3 6.5 7.6 S 1.0 1.6 1.4 1.0 1.2 1.1 1.2 1.0 1.7 0.9 Free swelling index 8. 0 7. 5 2 NC 8. 0 7. 5 7. 0 7. 5 8.0 2. 5 2 NO Heating value, Btu/lb 14, 160 13, 980 13, 440 13, 900 13, 430 13, 300 13, 750 13, 900 13, 680 13, 660

American Society of Testing Materials, Standard Test Method for the Determination of the Free Swelling Index of Coal,

ASTM Teit 13420-57.

2 NO=Noneaking.

It will be noted that pretreatment of the caking coal in accordance with the process of the invention, as in Tests Nos. 2 and 11 of the examples, resulted in formation of a char that flowed as freely as raw coal. On the other hand, inadequate treatment at the softening temperature, as in Tests Nos. 4, 6, 8 and results in formation of a char that is fused into one solid mass. In Tests Nos. 1, 3, 5, 7 and 9, the elevated temperature treatment was not sufficient to form the desired char.

It is apparent from the above data that successful pretreatment of caking coal to form a nonagglomerated char requires heating at a controlled rate to insure adequate treatment at the softening temperature of the coal prior to heating through the plastic temperature to form char.

What is claimed is:

1. A method of forming a nonagglomerated char from particles of cakiug coal, said particles having a size of at least about /a inch, which comprises heating said coal in a fixed bed to its softening temperature in flowing contact with a gas containing a small but effective concentration of oxygen, said oxygen concentration being in the range of about 0.5 to about 3.0 percent, and thereafter continuing said contacting while controlling the temperature of said coal so as to raise the temperature of said coal through its plastic range in not less than about 1 hour.

2. The method of claim 1 in Which the coal is held at its softening temperature for a period of about 1 to 3 hours.

3. The method of claim 1 in which the particle size of the caking coal is from about /8 to about 1 /2 inches.

4. The method of claim 1 in which the oxygen-com taining gas is passed through the bed of caking coal at a velocity of from about 0.6 to about 12 feet per second.

5. The method of claim 1 in which the oxygen-containing gas is a mixture of steam and oxygen.

6. The process of claim 1 wherein said step of controlling the temperature of said coal comprises maintaining said coal at its softening temperature for at least about 1 hour and thereafter rapidly heating said coal through its plastic range.

7. The process of claim 1 wherein said step of c011- trolling the temperature of said coal comprises heating said coal through its plastic range at a substantially uniform rate.

8. The process of claim 1 wherein said coal is contacted with said gas at an elevated pressure.

9. The method of claim 8 in which the pressure is about 300 p.s.i.g.

References Cited UNITED STATES PATENTS 1,767,778 6/1930 Trent 20l9 1,954,351 4/1934 Dornbrook et al. 20l9 2,167,099 7/1939 Benezech 201-9 X 2,336,151 12/1943 Kruppa 201-9 2,341,861 2/1944 Fuchs 20l9 2,805,189 9/1957 Williams 20l9 3,094,477 6/1963 Kruppa 20l9 FOREIGN PATENTS 770,930 3/1957 Great Britain.

JOSEPH SCOVRONEK, Primary Examiner. 

1. A METHOD OF FORMING A NONAGGLOMERATED CHAR FROM PARTICLES OF CAKING COAL, SAID PARTICLES HAVING A SIZE OF AT LEAST ABOUT 1/8 INCH, WHICH COMPRISES HEATING SAID COAL IN A FIXED BED TO ITS SOFTENING TEMPERATURE IN FLOWING CONTACT WITH A GAS CONTAINING A SMALL BUT EFFECTIVE CONCENTRATION OF OXYGEN, SAID OXYGEN CONCENTRATION BEING IN THE RANGE OF ABOUT 0.5 TO ABOUT 3.0 PERCENT, AND THEREAFTER CONTINUING SAID CONTACTING WHILE CONTROLLING THE TEMPERATURE OF SAID COAL SO AS TO RISE THE TEMPERATURE OF SAID COAL THROUGH ITS PLASTIC RANGE IN NOT LESS THAN ABOUT 1 HOUR. 